1. Field of the Invention
The present invention relates to an electric motor arrangement for a medical, more particularly dental, handpiece, more particularly a small dental motor, that is to say an electric motor of compact design which is provided more particularly for use in dental handheld devices. Such an electric motor arrangement is also designated hereinafter as “dental motor” or “small dental motor” for short.
2. Related Technology
More particularly, the invention relates to an electric motor arrangement provided for being connected via a coupling to a medical, more particularly dental, handpiece and angular piece, also called “handpiece” for short hereinafter, wherein the handpiece is designed for receiving a rotatably mounted tool, and wherein, when the electric motor arrangement is coupled to the handpiece as intended, a torque generated by the electric motor arrangement can be transmitted to the tool. A corresponding arrangement is known from DE 33 32 627 A1, for example. Furthermore, it can be provided, in particular, that a supply hose is connected by coupling so as to lie opposite the handpiece, with respect to the electric motor arrangement, which supply hose serves to supply the electric motor arrangement or the handpiece and has, for example, medium lines, by which media such as air and/or water for forming a spray can be transported. A power line and/or a light line can also be arranged in the supply hose.
Small dental motors should be sterilized more or less frequently depending on the application. This is being carried out more and more using class B sterilizers. In the course of chamber venting by means of pre-vacuum, the motor is repeatedly exposed to a reduced pressure of up to approximately 50 mbar abs. and alternately superheated steam at 134° C. This sterilization process attacks the insulating enamel of the copper wires, impregnating resins, adhesives and also potting compounds (silicone), used for fixing and protecting the stator winding, to an extreme degree, produces cracks in these materials and breaks down the latter, which ultimately leads to a lack of insulation and an inter-turn fault.
In order to obtain sterilization-resistant motors, it is necessary for the stator to be sheathed completely and impermeably with a sterilization-resistant high-temperature polymer (e.g. PEEK, PPS, LCP, PAI, PPSU, PSU, PES).
The prior art (KL 70/1702) discloses a stator wherein the winding is encapsulated with PPS by injection molding. Six cutouts for the medium line (tubes), from the supply hose connection side to the instrument side or handpiece side are present on the circumference. The magnetic return path is a separate component and not completely encapsulated by injection molding.
In order to obtain the required motor power, the distance between return path and permanent magnet has to be made small. There remains only limited space for the stator encapsulated by injection molding, which has the consequence that the plastic sheathing is made very thin and specifically is not fully closed in the region of the medium line. These imperfections in the plastic enclosure and the return path not encapsulated by injection molding drastically reduce the service life in the case of sterilization using saturated superheated steam and fractionated pre-vacuum.
From the so-called “Chirurgiemotor 550”, furthermore, a stator is known wherein a winding head is not sheathed with plastic. The superheated steam attacks the exposed enameled copper wires despite sealing with impregnating resin.
From the so-called system “COMFORTdrive” from the present applicant, a stator is known wherein the coil with enameled copper wires and also the soft-magnetic return path are completely encapsulated by injection molding and contact is made with the individual coil phases by means of contacts injection-molded tightly in the stator body. The medium tubes and the optical fiber rod for guiding light are situated outside the stator body encapsulated by injection molding in a segment-like cutout of the stator, which results in an asymmetrical stator body.
Furthermore, for ergonomic reasons it is desirable to be able to design a corresponding electric motor arrangement as compactly as possible or with a particularly small structural size. As low a weight as possible is also desirable against this background.